Technical Field
The present disclosure relates to a palladium(II) complex which catalyzes the Sonogashira coupling reaction efficiently under mild reaction conditions and a method of employing the palladium(II) complex to synthesize internal alkynes.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.
The Sonogashira coupling of aryl halides with aryl and alkyl alkynes provides a powerful tool for construction of the carbon-carbon bond between acetylenes and alkenes/arenes (Lui, C.; Bao, F.; Ni, Q. Arkivoc xi, 2011, 60. Guan, J. T.; Weng, T. Q.; Yu, G.; Liu, S. H. Tetrahedron Lett. 2007, 48, 7129. Komaromi, A.; Novak, Z. Chem. Comm. 2008, 4968. Huang, H.; Liu, H.; Jiang, H.; Chen, K. J. Org. Chem. 2008, 73, 6037. Gu, Z.; Li, Z.; Liu, Z.; Wang, Y.; Liu, C.; Xiang, J. Catal. Comm. 2008, 9, 2154. Casado, M. A.; Fazal, A.; Oro, L. A. Arab. J. Sc. Eng. 2013, 38, 1631, each incorporated herein by reference in their entirety). Alkynes are important because they are found in a wide range of natural products and other biologically active substances, and they are versatile intermediates for the production of materials for advanced engineering applications such as conducting polymers, non-linear optical devices and liquid crystals (Leadbeater, N. E.; Tominack, B. J. Tetrahedron. 2003, 44, 8653. Hamajima, A.; Isobe, M.; Org. Lett. 2006, 8, 1205. Mujahidin, D.; Doye, S. Eur. J. Org. Chem. 2005, 2689. Hajipour, A. R.; Zade, Z. S.; Azizi, G. Appl. Organometal. Chem. 2014, 28, 696, each incorporated herein by reference in their entirety).
The development of methods for incorporating C—C triple bonds into molecules remains an important area of research (Mathias, E.; Gregory, C. F. J. Am. Chem. Soc. 2003, 125, 13642, incorporated herein by reference in its entirety). In general, the Sonogashira coupling, which is the most commonly used method for the production of internal alkynes, is catalyzed by palladium complexes in combination with copper salts, and a large excess of an amine base (Chinchilla, R.; Najera, C. Chem. Rev. 2007, 107, 874, incorporated herein by reference in its entirety). However, the presence of copper(I) co-catalysts can result in the in situ formation of copper(I) acetylides leading to the oxidative homocoupling of alkynes (Siemsen, P.; Livingstone, R. C.; Diederich, F. Angew. Chem. Int. Ed. 2000, 39, 2633. Bakherad, M.; Keivanloo, A.; Bahramian, B.; Jajarmi, S. Appl. Catal. A: General 2010, 390, 135, each incorporated herein by reference in their entirety). To avoid homocoupling reactions, serious efforts have been made, including the employment of new, active palladium complexes as catalysts. However, there are problems associated with the copper-free systems such as the frequent requirement for high palladium catalysts loading, excess of base and rigorously dried organic solvent (Hundertmark, T.; Littke, A. F.; Buchwald, S. L.; Fu, G. C. Org. Lett. 2000, 2, 1729. Eckhardt, M.; Fu, G. C. J. Am. Chem. Soc. 2000, 39, 2632, each incorporated herein by reference in their entirety).
Through a comparison of available literature reports describing the use of phosphorous ligands in copper-free Sonogashira reactions, it was found that there are limited studies on the use of palladium-nitrogen catalyst systems (Tykwinski, R. R. Angew. Chem. Int. Ed. 2003, 42, 1566. Feuerstein, M.; Doucet, H.; Santelli, M. Tetrahedron Lett. 2004, 45, 8443. Liang, Y.; Xie, Y.; Li, J. J. Org. Chem. 2006, 71, 379. Valishina, E. A.; Silva, M. F. C.; Kinzhalov, M. A.; Timofeeva, S. A.; Buslaeva, T. M.; Haukka, M.; Pombeiro, A. J. L.; Boyarskiy, V. B.; Kukusukin, V. Y.; Luzyanin. K. V. J. Mol. Catal. A: Chemical. 2014, 395, 162. Soheili, A.; Walker, J. A.; Murry, J. A.; Dormer, P. G.; Hughes, D. L. Org. Lett. 2003, 5, 22, 4191. Liang, B.; Dai, M.; Chen, J.; Yang, Z. J. Org. Chem., 2005, 70, 391. John, A.; Shaikh, M. M.; Ghosh, P. Dalton. Trans. 2009, 10581. Dash, C.; Shaikh, M. M.; Ghosh, P. Eur. J, Inorg. Chem. 2009, 1608, each incorporated herein by reference in their entirety). Moreover, such catalyst systems utilize a high temperature, a longer reaction time, a relatively high palladium catalyst loading, a phosphine ligand, copper as co-catalyst, or a phase transfer agent (Najera, C.; Motto, J. G.; Karlstrom, S.; Falvello, L. R. Org. lett. 2003, 5, 1451. Buchmeiser, M. R.; Schareina, T.; Kempe, R.; Wurst, K. J. Organometal. Chem. 2001, 634, 39. Wang, D.; Denux, J.; Astruc, D. Adv. Synth. Catal. 2013, 355, 129. Lin, B-N.; Huang, S-H.; Wu, W-Y.; Mou, C-Y, Tsai, F-Y. Molecule 2010, 15, 9157. Aljarin, M.; Leonardo, C. L.; Lorente, P. L.; Raja, R.; Bautista, D.; Orenes, R-A. Dalton. Trans. 2012, 41, 12259, each incorporated herein by reference in their entirety). Furthermore, many of the reported phosphine-free and copper-free systems are limited to the coupling of aryl iodides with aryl alkynes (Ghiaci, M.; Zarghani, M.; Moeinpour, F.; Khojastehnezhad, A. Appl. Organometal. Chem. 2014, 28, 589, incorporated herein by reference in its entirety).
Therefore, an object of the present disclosure is to provide a palladium(II) catalyst effective for Sonogashira coupling reactions which are carried out in the absence of copper(I) catalysts and phosphine ligands. It is a further object to provide a method of employing the palladium(II) catalyst.